Process for producing a projection blackboard

Abstract

A projection blackboard having both of an excellent blackboard function and an excellent screen function, and a process for producing the same. The surface enamel layer that is an outermost layer of the enamel layers is formed by using a enameling upper glaze wherein at least titanium oxide coated particles, or a titanium oxide glaze together therewith is blended into a transparent mat glaze, so as to render the layer an enamel layer having a predetermined color tone, a surface characteristic that the Rz is from 5 to 25 μm and a reflective characteristic that the peak gain is 0.28 or more, or having these properties and a glossiness Gs (75°) of 1 to 30%. This makes it possible to produce a blackboard excellent in both of blackboard function and screen function. The titanium oxide coated particles are preferably particles wherein surfaces of mica particles are coated with titanium oxide.

The invention claimed is: 
     
       1. A process for producing a projection blackboard, comprising:
 coating a surface of a metallic substrate with an enameling lower glaze; 
 firing the coating to form an underlying enamel layer; 
 coating an underlying enamel layer with an enameling upper glaze in which at least titanium dioxide coated particles are blended into a transparent matte glaze, and at least one of black pigment, green pigment, and brown pigment or a combination of two or more thereof, as the pigment(s), is/are further added to the transparent matte glaze in accordance with a color tone of the blackboard; and 
 firing at 400 to 850° C. to form a surface enamel layer having a color tone having a brightness V according to JIS Z 8721-1993 of from 3.0 to 7.0, a surface roughness Rz according to JIS B 0601-2001 in a range of 5 to 25 μm, and a peak gain of 0.28 or more. 
 
     
     
       2. The process for producing a projection blackboard according to  claim 1 , wherein said enameling upper glaze is a glaze into which a titanium dioxide glaze or further a transparent gloss glaze is further blended. 
     
     
       3. The process for producing a projection blackboard according to  claim 2 , wherein said titanium dioxide coated particles are particles wherein surfaces of mica particles are coated with titanium dioxide. 
     
     
       4. The process for producing a projection blackboard according to  claim 2 , wherein said metallic substrate is a cold-rolled steel sheet, an aluminum plated steel sheet, or a Zn—Al alloy plated steel sheet. 
     
     
       5. The process for producing a projection blackboard according to  claim 1 , wherein said titanium dioxide coated particles are particles wherein surfaces of mica particles are coated with titanium dioxide. 
     
     
       6. The process for producing a projection blackboard according to  claim 5 , wherein said metallic substrate is a cold-rolled steel sheet, an aluminum plated steel sheet, or a Zn—Al alloy plated steel sheet. 
     
     
       7. The process for producing a projection blackboard according to  claim 1 , wherein said metallic substrate is a cold-rolled steel sheet, an aluminum plated steel sheet, or a Zn—Al alloy plated steel sheet. 
     
     
       8. The process for producing a projection blackboard according to  claim 1 , wherein the surface enamel layer has a color tone with a brightness according to JIS Z 8721-1993 being from 4.0 to 6.0. 
     
     
       9. The process for producing a projection blackboard according to  claim 1 , wherein the surface enamel layer has a surface roughness according to JIS B 0601-2001 of from 10 to 22 μm. 
     
     
       10. The process for producing a projection blackboard according to  claim 1 , wherein the surface enamel layer has a peak gain of 0.5 to 1.0. 
     
     
       11. The process for producing a projection blackboard according to  claim 1 , wherein the surface enamel layer has a 75-degree mirror plane glossiness according to JIS Z 8741-1997 of 1% TO 30%. 
     
     
       12. The process for producing a projection blackboard according to  claim 1 , wherein the surface enamel layer contains 2% to 40% by mass of the titanium dioxide coated particles. 
     
     
       13. The process for producing a projection blackboard according to  claim 1 , wherein the titanium dioxide coated particles have an average particle diameter of 5 μm to 80 μm. 
     
     
       14. A process for producing a projection blackboard, comprising:
 coating a surface of a metallic substrate with an enameling upper glaze in which at least titanium dioxide coated particles are blended into a transparent matte glaze, and at least one of black pigment, green pigment, and brown pigment or a combination of two or more thereof, as the pigment(s), is/are further added to the transparent matte glaze in accordance with a color tone of the blackboard; and 
 firing the coating at 400 to 850° C. to form a surface enamel layer having a color tone having a brightness V according to JIS Z 8721-1993 of from 3.0 to 7.0, a surface roughness Rz according to JIS B 0601-2001 in a range of 5 to 25 μm, and a peak gain of 0.28 or more. 
 
     
     
       15. The process for producing a projection blackboard according to  claim 14 , wherein said enameling upper glaze is a glaze into which a titanium dioxide glaze or further a transparent gloss glaze is further blended. 
     
     
       16. The process for producing a projection blackboard according to  claim 15 , wherein said titanium dioxide coated particles are particles wherein surfaces of mica particles are coated with titanium dioxide. 
     
     
       17. The process for producing a projection blackboard according to  claim 15 , wherein said metallic substrate is a cold-rolled steel sheet, an aluminum plated steel sheet, or a Zn—Al alloy plated steel sheet. 
     
     
       18. The process for producing a projection blackboard according to  claim 14 , wherein said titanium dioxide coated particles are particles wherein surfaces of mica particles are coated with titanium dioxide. 
     
     
       19. The process for producing a projection blackboard according to  claim 18 , wherein said metallic substrate is a cold-rolled steel sheet, an aluminum plated steel sheet, or a Zn—Al alloy plated steel sheet. 
     
     
       20. The process for producing a projection blackboard according to  claim 14 , wherein said metallic substrate is a cold-rolled steel sheet, an aluminum plated steel sheet, or a Zn—Al alloy plated steel sheet.